Answer this question truthfully
### Question: What causes Deep vein thrombosis?
### Response: Deep venous thrombosis (DVT) mainly affects the large veins in the lower leg and thigh. The clot can block blood flow and cause swelling and pain. When a clot breaks off and moves through the bloodstream, this is called an embolism. An embolism can get stuck in the brain, lungs, heart or another other area that can lead to severe damage.
Blood clots may form when something causes the flow of blood in the veins to slow or change.
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